1. Field of the Invention
The present invention relates to novel bacteria inhibiting halitosis or oral malodor emanating from the oral cavity. More specifically, the present invention relates to novel lactic acid bacteria that are isolated among microorganisms normally existing in the oral cavity of a person. These lactic acid bacteria are novel lactic acid bacteria belonging to genus Weissella that inhibit the proliferation of anaerobic bacteria producing volatile sulfur compounds by interacting with them and producing hydrogen peroxide under aerobic and anaerobic conditions.
2. Description of the Background
Halitosis or oral malodor is bad breath derived from the oral cavity and organs adjacent thereto, and many people suffer from halitosis in everyday life. About 85 to 90% of halitosis is originated from the oral cavity, especially, a rear part of the tongue. Major components of halitosis are volatile sulfur compounds, and about 90% of the total volatile sulfur compounds consist of hydrogen sulfide made from cysteine and methyl mercaptan made from methionine. These compounds are produced by anaerobic bacteria, and the rear part of the tongue is the most important inhabitation for the anaerobic bacteria. Since it is impossible to completely clean this part with saliva and there are many small crevices, the anaerobic bacteria can continuously survive in the rear part of the tongue. Although the production of volatile sulfur compounds by anaerobic bacteria is a major cause of halitosis, halitosis may also be caused by oral diseases such as tooth decay and periodontitis. Bacteria that produce hydrogen sulfide from cysteine include genus Peptostreptococcus, genus Eubacterium, genus Selenomonas, genus Centipeda, genus Bacteroides and genus Fusobacterium; and bacteria that produce methyl mercaptan from methionine include genus Fusobacterium, genus Bacteroides, genus Porphyromonas and genus Eubacterium. Especially, Fusobacterium nucleatum, Prevotella intermedia and Porphyromonas gingivalis are frequently found in the oral cavity of a halitosis patient. Genus Bacteroides, genus Porphyromonas and genus Prevotella are too similar to one another to such an extent that they have been previously known as belonging to the same genus. Many kinds of anaerobic bacteria are responsible for halitosis, but the representative bacteria for the development of halitosis are Fusobacterium nucleatum and Porphyromonas gingivalis. 
Since the most effective way to prevent halitosis is to inhibit the proliferation of anaerobic bacteria producing volatile sulfur compounds known as major components of halitosis, a method for removing tongue fur with a tongue scraper to eliminate substrates for the bacterial proliferation from the tongue, or for treating the tongue with a metal salt such as zinc chloride or a disinfectant such as alcohol or chlorhexidine to inhibit the production of volatile sulfur compounds by anaerobic bacteria has been previously employed. However, there are problems in that the metal salt and disinfectant inhibit the growth of other harmless oral microorganisms as well as halitosis-inducing anaerobic bacteria. Since they are not swallowed into the gullet, they do not reach a rear part of the tongue that is a place of concern in the development of halitosis. They are merely gargled in a front part of the oral cavity and then spat out of the mouth. Thus, there is a problem in that they cannot clean the rear part of the tongue which is the main place for the proliferation of halitosis-inducing anaerobic bacteria. Further, since they are diluted with saliva and swallowed into the gullet together with the saliva, their cleansing effects in the oral cavity last only for 20 minutes to 2 hours. Thereafter, anaerobic bacteria proliferate again in the oral cavity, thereby inducing halitosis again. Therefore, the metal salt and disinfectant used for decreasing halitosis are effective only in a short period of time.
Recently, there has been an attempt to inhibit the proliferation of anaerobic bacteria using lactic acid bacteria in vitro. The lactic acid bacteria are bacteria producing lactic acid as a final product by fermenting a carbohydrate, exist in the oral cavities and digestive tracts of a person and an animal, and are typically used for manufacturing a fermented food such as Kimchi or yogurt. The lactic acid bacteria used for the food industry include genus Enterococcus, genus Lactobacillus, genus Lactococcus, genus Leuconostoc, genus Streptococcus and genus Weissella. However, since these lactic acid bacteria are diluted with saliva and directly swallowed into the gullet when orally administered, there is a problem in that they are difficult to remain in the oral cavity. Further, lactic acid bacteria such as Lactobacillus acidophilus, Lactobacillus casei and Lactobacillus salivarius can inhibit the in vitro proliferation of anaerobic bacteria by producing a strong acid, but this strong acid produced by the lactic acid bacteria is neutralized by the buffering function of saliva in the oral cavity of a healthy person. Accordingly, it is hard to inhibit the bacterial proliferation. Furthermore, since the strong acid causes dental caries, the continuous administration of these bacteria may give rise to problems in oral hygiene.